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The population, which winters in several small reserves in Mexico, has experienced a wet and very cold winter, and illegal logging has also threatened their habitats.
These threats have combined to reduce the monarch population by as much as 50 to 60 percent, said Craig Wilson, a butterfly expert at Texas A&M University.
?There's a lot of reasons to be concerned,? Wilson said.
When they're wet, the butterflies are more vulnerable to cold weather. And logging around their habitats has exacerbated the problems with mudslides because there is little growth to hold the mud back.
Only 12 sightings so far
Mudslides near the monarch reserves of the Mexican state of Michoacan killed 40 people in February and damaged the trees where the butterflies breed and spend their winter months.
Last year, Texas observers had reported about 70 sightings across the state by this time, Wilson said, but there have so far been only 12 this year.
Part of the reason has been the cold weather ? the Southeast Texas region experienced one of its five coldest winters of the last century this year ? and the butterflies need temperatures of 70 degrees Fahrenheit or above to travel successfully. Wilson said he is also concerned that spring's late start has delayed the growth of milkweed plants, the only place where butterflies lay their eggs.
The development of new butterflies is essentially because it is usually the third or fourth generation of monarch butterfly that reaches Canada each summer.
And during their northward trek from Mexico to southern Canada, adult monarchs rely heavily on nectar food sources in Texas, Wilson said.
Texas residents can help by planting a small butterfly garden.
?It really is a case of, if you build it they will come,? Wilson said.
Re: 2010 may be a deadly year for monarch butterflies